Alarm system with radio alarm link and equipment-activating power line link

ABSTRACT

An alarm system has both radio and power line communication links between the protected premises and a monitoring station. Intrusion alarm monitoring equipment at the monitoring station is activated to respond to radio alarm signals from the protected premises by &#39;&#39;&#39;&#39;activate&#39;&#39;&#39;&#39; signals that originate at the protected premises and are transmitted over power lines to the monitoring station. The monitoring station signals back to the protected premises over the power lines the fact that it is &#39;&#39;&#39;&#39;armed&#39;&#39;&#39;&#39; or activated as to intrusion alarm signals from those premises, and also signals any intrusion alarm detected at said protected premises. The intrusion alarm transmitter or transmitters at the protected premises can send a radio alarm signal only in compliance with current F.C.C. requirements.

llnited States Patent 1191 1111 3,852,740

Haymes Dec. 3, 1974 [54] ALARM SYSTEM WITH RADKO ALARM 3,757,315 0 1073Birchficld c 111. 340 224 LINK AND EQUlPMENT-ACTWATING POWER LINE LINKPrimary Examiner-Glen R. Swann, Ill

' Attorney, Agent, or Firm-Oltman and Flynn [75] Inventor: IrvingHaymes, Tamarac, Fla. Y

[73] Assignees: Earl Yale Fine; Kenneth Borzage; ABSTRACT S0leyGoldberg; Steven Fine, part An alarm system has both radio and powerline comnte est o ch munication links between the protected premises and[22] Filed: AP 16, 1973 I a monitoring station. Intrusion alarmmonitoring equipment at the monitoring station is activated to respondto radio alarm signals from the protected prem- [21] Appl. No.: 351,164

ises by activate signals thatoriginate at the pro- [52] US Cl 340/416340/224 340/310 R tected premises and are transmitted over power lines g340/420 to the monitoringstation. The monitoring station sig- 51 1111.C1. G08b 25/00 back the Pmtected premises the Power [58] Field ofsearchm 340/224 416 420 310 R lines the fact that it is armed oractivated as to' in- 54 1 27 trusion alarm signals from those premises,andalso signals any intrusion alarm detected at said protected [56] IReferences Cited premises]. The tmtrugion alarm transmiter orgranslmiters a 6 pro 60 e premises can sen a ra 10 a arm UNITED STATESPATENTS signal only in compliance with current F.C.C. require- 1,698,7701 1929 0111 340/310 R mems 2,003,877 6/1935 Blatterman... 340/310 R2,547,024 4/1951 Noble 340/310 R 20 ClalmS, 3 Drawing Flames 3,540,04311/1970 Crosthwait 340/224 g "3'X-ALARMDEC0DERS. 2 i l ALARM *7;

o ALER.

gggg J EMERGENCY 2? AuoIaEALAm:

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,- i I I POLARITY 1 I REVERSER. 5 i I 24 2: FI/F2 I ii'f'iron. I I6- KEYPLUG. I5 KEY JACK, L I 1 1a In 1 i I PULSE l OSCILLATOR. I7 L? i i 1i|.l|lli 12 14 .42 I3 I 1 1 1 11 WINDOWALARM 00m ALARM 3 gffggf FIREALARM TRANSMITTER. TRANSMITTER. TRANSMITTER TRAAGMITTER. 1 1 1 1 1 a L Ll I I0 PROTECTED PREMISB.

PATENTEL DEC 31974 sum 1 or 2 ALARM DECODERS.

POLICE DEPT FIRE DEPT AUTO. DIAIER.

AUDIBLE KZ'ARM.

LN 7/ ALARM.

ALARM DETECTION 8 DISTRIBUTION PANEL.

BURGLARK EMERGENCY FIRE.

INDICATOR 8 BELL TRANSMITTER.

INHIBIT RADIO RECEIVER.

KEY RECEIVER.

ACTIVATE J R. mm AT w W 5 M R L R. L N o 0 E m m H mm m F FT m Rn ma 0mx us CO PO f V'- 1 m n m; Q m m E I I M H H M\| mwwm 4 K R a M M: W 44| EAm Mm mx kfl m R mm M. 2 W RM a mm m a J 1 R m. mm L Mm F IIL L IOPROTECTED PREMISES.

PATENIEL 3W 3,852,740

sum 20F 2 SELECTIVE CARRIER DE MODULATOR. LIMI TE R.

FROM AMPLIFIER. mIIgER I i I I I 2 g 2 -54 II\K I F2 DECODER l g 3 3 Q59 i I 64 I 1 58 *W'I' fi 1 l 55 I I $2127 I I e3 E2 I 65 61x c g IMODULE. 1 I

I' I' IT 0 T 85 5x33557 01; OSCILLATOR.

ALARM SYSTEM WITH RADIO ALARM LINK AND EQUIPMENT-ACTIVATING POWER LINELINK SUMMARY OF THE INVENTION This invention relates to an alarm systemfor responding to various types of alarm conditions, particularly in anindustrial plant, a museum or other public building, or a privateestate, condominium, apartment building, or house where security fromburglars, fire or other hazards is particularly important.

In broad outline, the present system has radio alarm transmitters at ornear the premises to be protected from intrusion and intrusion alarmmonitoring equipment at a different location which, for purposes of thisdiscussion, may be called the security headquarters. The monitoringequipment is conditioned to respond to intrusion alarm signals at theprotected premises by an action initiated there by a custodian. Forexample, at the end of the workday in an industrial plant all the doorsand windows may be closed, and from then until the beginning of the nextworkday they should remain closed. During this time period when nobodywould open a door or window except an unwelcome intruder, the systemshould be activated to detect such intrusions and it is the custodiansresponsibility to do this. The

present system has provision for activating the intrusion alarmmonitoring equipment at the security headquarters by signals transmittedover power lines from the premises to be protected. Also, this systemhas provision for signalling back over the power lines from the securityheadquarters the fact thatthe system has been activated for intrusionsat those premises or that a door or window is open there, so that thecustodian will be so informed. Also, the security headquartersautomatically notifies the custodian over the power lines whenever anintrusion alarm condition occurs at his premises. The window and dooralarm transmitter or transmitters in the present system have atamper-proof arrangement for insuring that these transmitters complywith current F.C.C. regulations governing the duration of intermittentfon" and off" broadcast intervals.

It is a'principa l object of this invention to provide a novel'andimproved alarm system.

Another object of this invention is to provide such an alarm systemwhich has both a radio link and a power line link between the premisesto be protected and a station where alarm monitoring equipment islocated.

Another object of this invention is to provide a hybrid alarm systemwith both radio and power line links which has all the versatility ofprevious all-wire alarm systems.

Another object of this invention is to provide such an alarm system inwhichv the power line link is used to activate the equipment at themonitoring station to respond to intrusion alarm signals from theprotected premises, and to signal back to the protected premises thatsuch activation has occurred.

Another object of this invention is toprovide such an alarm system inwhich the power line link is used to signal from the monitoring stationback to the protected premises when an alarm condition has occurred atsaid protected premises.

Another object of this invention is to provide a novel and improvedalarm system having a radio alarm link with provision for insuring thatthe intrusion alarm signal transmissions comply with current F.C.C.requirements.

Further objects and advantages of this invention will be apparent fromthe following detailed description of a presently-preferred embodimentthat is described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 illustrates the present alarmsystem schematically, primarily in block diagram form;

FIG. 2 is a circuit diagram of equipment at the monitoring station inFIG. 1 for receiving coded signals coming over power lines from theprotected premises; and

FIG. 3 is a circuit diagram showing schematically a burglar alarmtransmitter at the protected premises in the present system.

DESCRIPTION OF THE PREFERRED EMBODIMENT OVERALLSYSTEM FIG. 1

Referring to FIG. 1, at the protected premises 10 are located one ormore window alarm transmitters 11, which transmit a distinctivelymodulated radio signal whenever a window is open there, and one or moredoor alarm transmitters 12, which transmit a distinctively modulatedradio signal whenever a door is open there. These window and door alarmtransmitters 11 and 12 are described in more detail hereinafter withreference to FIG. 3. In some situations, a single transmitter maytransmit both window alarms and door alarms.

Also located at the protected premises are one or more fire alarmtransmitters 13, which broadcast a distinctively modulated radio signalwhenever a tire is detected, and one or more emergency alarmtransmitters 14, which broadcast a distinctively modulated radio signalwhenever a'particular type of emergency occurs on the premises, such asa malfunction of refrigerators or freezers in a food store, for example,or a signal purposely initiated by a person in need of help.

The carrier frequency is the same for all the different types of radioalarm signals. The modulation for door alarms may be the same as forwindow alarms, since both indicate a burglary or they may be different.The respective modulations for emergency alarms and fire alarms aredifferent from each other and from the door and window alarms since eachcalls for a different type of response.

Also located at the protected premises is a key jack 15 for receiving aportable key plug 16 carried by a custodian. The key jack 15 isconnected to an oscillator 17 which produces pulses at a frequency F lor at a different frequency F2, as explained hereinafter. The oscillatorl7 pulse-modulates a carrier signal oscillator 18, whose output isconnected through a conventional wall socket (not shown) to a volt powerline 19.

For the sake of simplicity, this power line 19 is shown connecteddirectly to the monitoring station 20 of the present system, which isremote from the protected premises and which may serve a number ofdifferent protected premises. However, it is to be understood that thissimplified, direct power line connection might will be transmitted overpower lines from the protected premises to the monitoring station 20.

At the monitoring station, the pulse-modulated carrier signal comingfrom the protected premises 10 operates a key receiver 21 which willdetermine from this incoming signal whether or not the burglar alarmmonitoring equipment at the monitoring station should be armed" as tothose protected premises (i.e., activated or conditioned to respond tovarious door or window alarm conditions that may occur at thoseprotected premises).

The key receiver 21 controls a transmitter 22 at the monitoring stationwhose output is connected to a conventional wall power socket there tosend a signal over the power lines 19 back to a decoder 23 at theprotected premises 10. The out-put from this decoder is a DC. signalwhose plurality is reversed by a polarity reverser 24 before beingapplied to terminal 25 of the key jack 15, which is engaged by acorresponding terminal 26 on the key plug 16 when the latter is insertedin the key jack. When such insertion is made, another terminal 27 on akey plug contacts the grounded key jack terminal 28.

A light emitting diode 29 in the key plug is connected across terminals26 and 27 to be energized by the decoded signal coming back over thepower lines from the transmitter 22 at the monitoring station such that:

1. if a continuous, unmodulated carrier signal is received from themonitoring station transmitter 22, the light emitting diode 29 will beon continuously;

2. if the carrier signal received from the transmitter 22 is pulsemodulated, the light emitting diode 29 will flash on and off, whichindicates that the protected premises 10 are not secure, such as due toa door or window being open; and

3. if no carrier signal is received from the monitoring stationtransmitter 22, the light emitting diode will be off, which indicatesthat the entire burglar alarm system is disarmed for these protectedpremises.

Also, a horn, buzzer or other audible warning device (not shown) may beconnected to a suitable decoder plugged into any power outlet at theprotected premises to sound an alarm at the protected premises only ifthe carrier signal from the monitoring station transmitter 22 ispulse-modulated.

The monitoring station also has a radio receiver 30 which receives thealarm signals transmitted by any of the alarm transmitters 11-14 at anyprotected premises 10. The incoming radio-transmitted alarm signal isapplied to alarm decoders 31 which may differentiate among theemergency, fire and window or door (burglary) radio alarm signals. Inone practical embodiment, each decoder is a Signetics tone decoder phaselocked loop, Model SE/NE 567, as disclosed in the product manual ofSignetics Corporation, copyright 1972, pages 219-228.

The decoded alarm signal is applied to an alarm detection anddistribution panel 32 at the monitoring station, one of whose functionsis to signal an appropriate recipient that a predetermined alarmcondition has occurred at the protected premises 10. For example, thepolice may be notified of a door-open or window-open alarm condition,and the fire department may be notified of a fire alarm condition atthese premises. A private security service may be notified by telephonethrough an automatic dialer that an emergency alarm condition hasoccurred at the protected premises. In one practical embodiment, thealarm detection and distribution panel 32 is a Model 12-240 alarm,manufactured by Design Controls, Inc., 111 Cantiague Rock Road,Westbury, N. Y. 1 1590, and shown in that companys drawing no. 500-541,revision E, dated Aug. 4, 1971, and supplied to installers of suchalarms, including applicant, prior to the filing date of the presentapplication.

The monitoring station 20 is armed, or activated, as to a particularprotected premises 10 by turning on circuitry in the panel 32 to signalthe police and to operate the automatic dialing equipment and theaudible alarms. Preferably, the monitoring station 20 is armedcontinuously at all times for emergency and fire alarms from theprotected premises, and the alarm signalling for such conditions is notunder the control of the custodians key plug 16.

PROTECTED PREMISES Referring again to the equipment at the protectedpremises 10 in FIG. 1, when the key plug 16 is inserted into the keyjack 15, an end terminal 33 on the key plug engages a spring-contactterminal 34 on the key jack which is connected to a control terminal 17aof the pulse oscillator 17. A pair of resistors 35 and 36 in the keyplug are connected between its end terminal 33 and the terminal 27 whichis grounded when the key plug is inserted into the key jack. Thejuncture 37 between resistors 35 and 36 is connected to the mobilecontact 38 of a manually operable switch in the key plug. This switchhas a fixed contact 39 that is connected directly to terminal 27. Whenswitch 38, 39 is closed it shorts out resistor 36. Switch 38, 39 is anormally-open switch that returns to its open condition as soon as itsmanually operated actuator is released.

The key jack has a normally-open switch 40, 41 with a fixed contact 41that is grounded and a mobile contact 40 that is connected to thenegative terminal of a battery 42. The mobile switch contact 40 issuitably coupled mechanically to the key jack terminal 34 through anelectrically insulating coupling designated schematically by the dashedline 43, such that switch 40, 41 closes when the key plug 16 is insertedinto the key jack 15.

All of the alarm transmitters 11-14 at the protected premises areenergized at all times, irrespective of whether the key'plug 16 is inthe key jack for those premises. Therefore, each of these transmittersis ready continuously to transmit an alarm signal to the monitoringstation at all times. As already stated, the monitoring station 20 isarmed at all times to respond to emergency and fire alarm signals fromthe protected station, but it is armed to respond to intrusion alarmsignals only after the key plug 16 is inserted in the key jack 15 atthose premises.

The pulse oscillator 17 at the protected premises is an intergratedcircuit of known design that is capable of generating pulses atdifferent frequencies, depending upon the voltage at its controlterminal 17a. In the present system, this control voltage at terminal1711 may have either of two values, and the output pulse frequency ofthe oscillataor may be either of two values, F1 or F2.

The positive terminal of battery 42 is connected to a second terminal17b of the pulse oscillator to provide the power supply for thisoscillator when switch 40, 41

in the key jack is closed. The voltage at the firstmentioned terminal17a of this oscillator determines its pulse frequency, and this voltagedepends 1 upon whether or not the resistor 36 is shorted out. Thus, withkey plug 16 inserted into the key jack 15 and the manual switch 38, 39in the key plug open, the oscillator terminal 170 will be connected toground through the series-connected resistors 35 and 36., and itsvoltage will be at the higher of two values, and the pulse oscillatorfrequency will be F1. However, when the manual switch 38, 39 in the keyplug is closed, the oscillator terminal 17a will be connected to groundthrough resistor 35 only (resistor 36 being short-circuited), and itsvoltage will be at the lower of two values, and the pulse oscillatorfrequency will be F2.

KEY RECEIVER AT MONITORING STATION FIG. 2 illustrates schematicallyimportant components of the key receiver 21 at the monitoring station20. The pulse-modulated carrier signal from the protected premises It)comes in over the power lines 19 to a selective carrier amplifier 50,which amplifies this carrier, and then isdemodulated in a demodulator 51and limited in a limiter 52 before being applied to one or more similarkey detecting blocks Ka, Kb, Kc, etc., one for each different protectedpremises in the system.

The key detecting block Ka for the particular protected premises It) inFIG. I is shown as comprising two frequency sensitive decoders, an F1decoder 53 and an F2 decoder 54. Each of these decoders is an integratedcircuit with eight terminals, terminal 3 being the input terminal andterminal 8 being an output terminal. Each decoder is the solidstateequivalent of a reed relay, responding only to a particularfrequency, F1 or F2. Each decoder may be a Signetics Corporation ModelSE/NE 567 decoder, as already referred to.

Terminal 8 of the F1 decoder 53 is connected through a resistor 55 tothe positive terminal of a battery 56 and is connectedthrough acapacitor 57 to the grounded negative terminal of this battery. Terminal8 of the F1 decoder is connected through a resistor 58 and diode 59 toterminal 1 of the F2 decoder 54. Normally, terminal 8 of the F1 decoderand terminal 1 of the F2 decoder are at the positive battery voltage,and this inhibits the F2 decoder 54 from responding to an F2 signal.However, when the F1 decoder receives an F1 signal, the voltage at itsterminal 8 drops to zero, as does the voltage at terminal 1 of the F2decoder 54, so that now the F2 decoder is no longer inhibited and it canrespond to an F2 input signal at its terminal 3. Such an F2 input signalat terminal 3 of decoder 54 produces a signal at its output terminal 8that operates a sequential relay (not shown) for arming the monitoringstation '20 as to intrusion alarm signals from these premises by turningon power supplies for circuits in panel 32 for police signalling,operating the automatic dialer, and sounding audible alarms. Thissequential relay is energized by the first signal it receives from theF2 decoder, and it is deenergized by the next signal it will receivefrom the F2 decoder, as described hereinafter.

With this arrangement, to arm, or activate, the system as to intrusionalarm signals from these protected premises, the monitoring station mustreceive over the power lines 19 from the protected premises the carrierpulse-modulated by F1 and then the same carrier pulsemodulated by F2,and in that order (Fl preceding F2).

Otherwise, the F2 decoder 54 will remain inhibited, and the system armrelay will not be energized.

The F1 decoder 53 at the monitoring station has a narrow pass-band whosecenter frequency is determined by the values of a capacitor 60, anadjustable re'-- sistor 61, and a resistor 62 which is part of a keycode module 63.

Similarly, the F2 decoder 54 has a narrow pass band whose centerfrequency is determined by a capacitor 64, an adjustable resistor 65,and a resistor 66 which also is part of the key code module 63.

The key code module 63 correspondsto the pulse frequencies F1 and F2,whichare assigned to only one protected premises, as determined by theresistors 35 and 36 in the key plug 16 for those premises. Therefore,each key code module 63 at the monitoring station is frequency-matchedto a particular key plug for a certain protected premises.

Each of the other key detecting blocks Kb, 'Kc, etc., has circuitryidentical to that of the block Ka, except that the resistors in-therespective key code modules are different, so that each block Kb, Kc,etc. is frequency-tuned to only the two different modulatingfrequencies, F1 and F2, that are assigned to a particular protectedpremises. The carrier signals coming over the power lines from thedifferent protected premises are all at the same frequency.

Resistor 55 and capacitor 57 provide a time-delay circuit for preventingthe F2 decoder 54 from being inhibited again until about 250milliseconds after the F1 input signal disappears from the F1 decoder53. This is ample time for the F2 decoder 54 to respond to the F2 signaland energize the sequential relay for panel 32.

When the system is to be armed to respond to the window and door alarmtransmitters at a particular protected premises, the key plug switch 38,39 is open when the key plug 16 for those premises is inserted into thekey jack 15, so that the carrier signal transmitted from these protectedpremises will be modulated first by the F1 pulses. Then, when the keyplug switch 38, 39 is closed momentarily, this carrier will now bemodulated by the F2 pulses, so as to operate the system arm relaythrough the F2 decoder 54. However, as already explained, this actioncan take place only if the F2 pulses have been preceded by the F1pulses. The key plug switch 38, 39 re-opens automatically when releasedmanually, so asto re-transmit the Fl-modulated carrier to the keyreceiver 21 and thereby condition the F2 decoder in the key receiver torespond to the F2 modulation signal the next time the key plug switch38, 39 is closed.

If all the doors and windows at the protected premises are closed whenthe foregoing action takes place, then none of the door and windowtransmitters 11 and 12 will broadcast an intrusion alarm signal to thereceiver 30 at the monitoring station. However, if at this time there isan open window or door at the premises to be protected, the monitoringstation cannot be armed or activated as to those premises until thiscondition is corrected. Also, a distinctive signal will be transduce aninhibit" signal on line 70 (FIG. 1) that is applied to terminal 1 of theF2 decoder 54 in the key receiver 21, so as to prevent the F2 decoderfrom responding to the FZ-pulse modulated carrier transmitted from thepremises over the power lines 19 to the monitoring station.Consequently, the monitoring station cannot now be armed to respond tointrusion alarm signals from these premises.

The instruction alarm signal received by the receiver 30 at themonitoring station also causes panel 32 to produce on line 71 a signalthat is applied to the transmitter 22 to cause the latter to transmit apulsemodulated carrier over the power lines 19 back to the premises 10which, after being decoded, produces an intermittent flashing of thelight emitting diode 29. This is a visual signal to the custodian thatthere is a door or window open at these premises.

When all the doors and windows have been closed, the custodian closesthe key plug switch 38, 39, and the system will become armed as to thesepremises, as described.

When such arming takes place, the alarm signal on line 71 is removed andthe transmitter 22 at the monitoring station sends a continuous carriersignal over the power lines 19 back to the premise 10. This carrier,after being decoded, is applied to the light emitting diode 29 toprovide continuous illumination, which tells the custodian that thesystem is armed as to these premises and that no intrusion alarmcondition exists there.

If, after the monitoring station has been armed as to these premises, anintrusion alarm signal is transmitted to the receiver 30 at themonitoring station, it will produce on line 71 a pulse modulationcontrol signal to cause the light emitting diode to flash on and offagain.

When the custodian wants to disarm" the system as to intrusion alarmsignals originating at these premises 10 (such as at the beginning ofawork day in an industrial plant), first he closes the key plug switch38, 39 to again apply the F2 modulation to the carrier that istransmitted from the premises 10 over the power lines 19 to themonitoring station 20. The resulting output signal at terminal 8 of theF2 decoder 54 in the key receiver 21 energizes the sequential relay soas to remove the power for the circuits in panel 32 that signal thepolice, the automatic dialer and the audible alarms in the event of anintrusion alarm. Then the custodian removes the key plug from the keyjack.

DOOR OR WINDOW ALARM TRANSMITTER FIG. 3

FIG. 3 illustrates schematically a door/or window alarm transmitter atthe protected premises 10 in FIG. 1. There may be a single transmitterfor all doors and windows to be monitored at these premises, or a singletransmitter for all windows and a single transmitter for all doorsthere, as shown in FIG. 1, or various other- I combinations oftransmitters for different windows and doors at these premises.

This transmitter complies with the current F.C.C. requirement that thebroadcast interval be not longer than I second. and followed by a silentperiod of 30 seconds or more.

In FIG. 3 the transmitter is shown under the control of threeseries-connected sensor switches 80, 81 and 82, each associated with arespective door or window,

and each closed whenever that door or window is closed. Any desirednumber of such series-connected sensor switches may control a particularalarm transmitter. I

The sensor switches are connected in series between ground and the baseof transistor Q1, whose emitter is grounded and whose collector isconnected directly to the base of a second transistor Q2. The emitter ofO2 is connected directly to the positive terminal of a battery B andalso is connected to the base of 01 through a resistor 83.

The collector of O2 is connected through a seriesconnected diode 84 andcapacitor 85 to the base of Q1. A resistor 86 is connected betweenground and the juncture between diode 84 and capacitor 85.

The collector of Q2 is connected to the input of an encoder modulator 87whose output is connected to an RF. oscillator 88 coupled to a broadcastantenna 89.

In the operation of this transmitter, as long as all of the sensorswitches 80, 81 and 82 remain closed, both transistors Q1 and Q2 willremain off.

Whenever any one of the sensor switches 82 is opened, the base currentof transistor Q1 turns on, causing current to flow from the collector tothe emitter of 01. This turns on the base current in transistor Q2, andthe resulting emitter-collector current in Q2 operates the encodermodulator 87 so that the antenna 89 broadcasts a coded,amplitude-modulated radio signal that identifies this window/door alarmtransmitter at these particular protected premises. Preferably, thecarrier frequency of this radio signal is about 300,000,000 Hz, and themodulation signal frequency is in the supersonic range. This radiosignal will be picked up by the receiver 30 at the monitoring station(FIG. 1).

This coded signal transmission lasts only 1 second or less each time.During this 1 second or less, the capacitor will become charged throughdiode 84 enough to turn off the base current in Q1, thereby turning offQ1 and then turning off Q2. Capacitor 85 discharges through resistor 86,and the time constant provided by these circuit elements is such that Q1and Q2 remain off for thirty seconds or more. At the end of this period,transistors Q1 and Q2 will turn on again (if one of the sensor switches80-82 is still open) for the l second-orless on interval, and then theywill turn off again for the 30-second-or-more off period. During thisoff period, a repeated opening and closing of any of the sensor switches80-82 will have no effect. Instead the transmitter will remain off forthe full period of 30 seconds or more, so as to insure compliance withthe F.C.C. requirement mentioned hereinbefore.

The receiver 30 at the monitoring station includes suitable circuitryfor retaining the intermittentlybroadcast signal during the alarmtransmitters off periods.

It is to be understood that various modifications may be made in thesystem disclosed without departing from its'essential principles.

I claim:

1. In an alarm system having:

a monitoring station with alarm monitoring equipa protectedpremiseswhich is interconnected with the monitoring station throughelectrical power lines;

a radio link comprising one or more radio transmitters at the protectedpremises for transmitting an intrusion alarm signal when an intrusionalarm condition is detected there, and a radio receiver at themonitoring station for receiving said radio alarmsignals and operativelycoupled to said alarm monitoring equipment to actuate the latter when aradio alarm signal is received;

and a power line link comprising means selectively operable at theprotected premises for transmitting over power lines to the monitoringstation signals for activating the alarm monitoring equipment there torespond to intrusion alarm signals broadcast from the protectedpremises;

the improvement wherein said power line link further comprises means atthe monitoring station for transmitting over power lines to theprotected premises signal information as to whether the alarm monitoringequip ment there is activated to respond to intrusion alarm signalsbroadcast from said protected premises.

2. An alarm system according to claim 1, wherein said transmitting meansat the monitoring station is operative to transmit over power lines tothe protected premises a distinctive signal which tells that anintrusion alarm condition exists at said protected premises.

3. An alarm system according to claim 1, and further comprising signalindicator means at the protected premises for responding to the powerline signal coming from the monitoring station.

4. An alarm system according to claim 3, and further comprising:

means for modifying said last-mentioned signal when the radio receiverat the monitoring station receives an intrusion alarm signal from saidprotected premises.

5. An alarm system according to claim 4, wherein said transmittingmeansat the monitoring station transmits a distinctive carrier signalover the power lines to said protected premises which is unmodulated inthe absence of an intrusion alarm signal received from said protectedpremises and which is modulated when such reception occurs;

and said means at the protected premises for responding to saidlast-mentioned signal produces different indications for unmodulated andmodulated signals, respectively.

6. In an alarm system having:

a monitoring station with alarm monitoring equipment; v

a protected premises which is interconnected with the monitoring stationthrough electrical power lines;

a radio link comprising one or more radio transmitters at the protectedpremises for transmitting on intrusion alarm signal when an intrusionalarm condition is detected there, and a radio receiver at themonitoring station for receiving said radio alarm signals andoperatively coupled to said alarm monitoring equipment to actuate thelatter when a radio alarm signal is received; 7

and a power line link comprising means selectively operable at theprotected premises for transmitting over power lines to the monitoringstation signals for activating the alarm monitoring equipment there torespond to intrusion alarm signals broadcast from the protectedpremises;

the improvement wherein said selectively operable means at the protectedpremises comprises;

means for applying a carrier signal to the power lines to be transmittedto the monitoring station; 5 means for modulating said carrier signal ateither of two different frequencies; and selectively operable means foractivating said modulating means and for selecting the modulatingfrequency.

7. An alarm system according to claim 6, and further comprising means atthe monitoring station for receiving the modulated carrier signal comingover the power lines from said protected premises and for respondingseparately to the two different modulating frequencies to condition thealarm monitoring equipment at the monitoring station to respond tointrusion alarm signals broadcast by radio from said protected premises.

8. An alarm system according to claim 7, wherein said means forresponding separately to the two different modulating frequencies issensitive to the sequence in which said two different modulatingfrequencies are transmitted over the power lines from said protectedpremises to the monitoring station.

9. An alarm system according to claim 8, wherein said means forresponding separatelyto the two different modulating frequenciescomprises;

a first decoder that is sensitive substantially only to a firstmodulating frequency, F1;

a second decoder that is sensitive substantially only to a secondmodulating frequency, F2;

means coupled to the output of said second decoder for conditioning thealarm monitoring equipment at the monitoring station to respond tointrusion alarm signalsfrom said protected premises in re sponse to theactivation of the second decoder by an incoming F2 signal;

and circuit means interconnecting said first and second decoders forinhibiting the second decoder from being activated by an incoming F2signal until after said first decoder has received an F1 signal.

and selectively operable means at the protected premises fortransmitting signals over the power lines to the monitoring station toactivate the monitoring equipment there to respond to intrusion alarmsignals from the protected premises;

the improvement which comprises:

a transmitter at the monitoring station for transmitting a signal overthe power lines to the protected premises when the alarm monitoringequipment at the monitoring station is conditioned to respond tointrusion alarm signals from the protected premises;

and means at the protected premises for responding to saidlast-mentioned signal. 12. An alarm system according to claim 11, andfurther comprising:

means for modifying said last-mentioned signal when the alarm monitoringequipment responds to an intrusion alarm signal from said protectedpremises.

13. An alarm system according to claim 12, wherein said transmitter atthe monitoring station transmits a distinctive carrier signal over thepower lines to said protected premises which is unmodulated in theabsence of a response by said monitoring equipment to an intrusion alarmsignal from said protected premises and which is modulated when such aresponse occurs;

and said means at the protected premises for responding to saidlast-mentioned signal produces different indications for unmodulated andmodulated signals, respectively.

14. An alarm system according to claim 13, wherein said selectivelyoperable means at the protected premises may be operated to de-activatethe alarm monitoring equipment at the monitoring station from respondingto intrusion alarm signals at said protected premises. v

15. In an alarm system having:

intrusion alarm condition-signalling means at a protected premises;

alarm monitoring equipment for receiving alarm signals at a monitoringstation which is linked to the protected premises through electricalpower lines;

modulating means and for selecting the modulating frequency.

16. An alarm system according to claim 15, and further comprising meansat the monitoring station for receiving the modulated carrier signalcoming over the power lines from said protected premises and forresponding separately to the two different modulating frequencies tocondition the alarm monitoring equipment at the monitoring station torespond to alarm signals from said protected premises.

17. An alarm system according to claim 16, wherein said means forresponding separately to the two different modulating frequencies issensitive to the sequence in which said two different modulatingfrequencies are transmitted over the power lines from said protectedpremises to the monitoring station.

18. An alarm system according to claim 17, wherein said means forresponding separately to the two different modulating frequenciescomprises:

a first decoder that is sensitive substantially only to a firstmodulating frequency, F1;

a second decoder that is sensitive substantially only to a secondmodulating frequency, F2;

means coupled to the output of said second decoder for conditioning thealarm monitoring equipment at the monitoring station to respond tointrusion alarm signals from said protected premises in response to theactivation of the second decoder by an incoming F2 signal;

and circuit means interconnecting said first and second decoders forinhibiting the second decoder from being activated by an incoming F2signal until after said first decoder has received an F1 signal.

selectively operable means at the protected premises for transmittingsignals over the power lines to the monitoring station to activate themonitoring equipment there to respond to intrusion alarm signals fromthe protected premises; the improvement which comprises means forpreventing said selectively operable means for activating the monitoringequipment at the monitoring station when an intrusion alarm conditionalready exists at said protected premises.

1. In an alarm system having: a monitoring station with alarm monitoringequipment; a protected premises which is interconnected with themonitoring station through electrical power lines; a radio linkcomprising one or more radio transmitters at the protected premises fortransmitting an intrusion alarm signal when an intrusion alarm conditionis detected there, and a radio receiver at the monitoring station forreceiving said radio alarm signals and operatively coupled to said alarmmonitoring equipment to actuate the latter when a radio alarm signal isreceived; and a power line link comprising means selectively operable atthe protected premises for transmitting over power lines to themonitoring station signals for activating the alarm monitoring equipmentthere to respond to intrusion alarm signals broadcast from the protectedpremises; the improvement wherein said power line link further comprisesmeans at the monitoring station for transmitting over power lines to theprotected premises signal information as to whether the alarm monitoringequipment there is activated to respond to intrusion alarm signalsbroadcast from said protected premises.
 2. An alarm system according toclaim 1, wherein said transmitting means at the monitoring station isoperative to transmit over power lines to the protected premises adistinctive signal which tells that an intrusion alarm condition existsat said protected premises.
 3. An alarm system according to claim 1, andfurther comprising signal indicator means at the protected premises forresponding to the power line signal coming from the monitoring station.4. An alarm system according to claim 3, and further comprising: meansfor modifying said last-mentioned signal when the radio receiver at themonitoring station receives an intrusion alarm signal from saidprotected premises.
 5. An alarm system according to claim 4, whereinsaid transmitting means at the monitoring station transmits adistinctive carrier signal over the power lines to said protectedpremises which is unmodulated in the absence of an intrusion alarmsignal received from said protected premises and which is modulated whensuch reception occurs; and said means at the protected premises forresponding to said last-mentioned signal produces different indicationsfor unmodulated and modulated signals, respectively.
 6. In an alarmsystem having: a monitoring station with alarm monitoring equipment; aprotected premises which is interconnected with the monitoring stationthrough electrical power lines; a radio link comprising one or moreradio transmitters at the protected premises for transmitting onintrusion alarm signal when an intrusion alarm condition is detectedthere, and a radio receiver at the monitoring station for receiving saidradio alarm signals and operatively coupled to said alarm monitoringequipment to actuate the latter when a radio alarm signal is received;and a power line link comprising means selectively operable at theprotected premises for transmitting over power lines to the monitoringstation signals for activating the alarm monitoring equipment there torespond to intrusion alarm signals broadcast from the protectedpremises; the improvement wherein said selectively operable means at theprotected premises comprises; means for applying a carrier signal to thepower lines to be transmitted to the monitoring station; means formodulating said carrier signal at either of two different frequencies;and selectively operable means for activating said modulating means andfor selecting the modulating frequency.
 7. An alarm system according toclaim 6, and further comprising means at the monitoring station forreceiving the modulated carrier sigNal coming over the power lines fromsaid protected premises and for responding separately to the twodifferent modulating frequencies to condition the alarm monitoringequipment at the monitoring station to respond to intrusion alarmsignals broadcast by radio from said protected premises.
 8. An alarmsystem according to claim 7, wherein said means for respondingseparately to the two different modulating frequencies is sensitive tothe sequence in which said two different modulating frequencies aretransmitted over the power lines from said protected premises to themonitoring station.
 9. An alarm system according to claim 8, whereinsaid means for responding separately to the two different modulatingfrequencies comprises; a first decoder that is sensitive substantiallyonly to a first modulating frequency, F1; a second decoder that issensitive substantially only to a second modulating frequency, F2; meanscoupled to the output of said second decoder for conditioning the alarmmonitoring equipment at the monitoring station to respond to intrusionalarm signals from said protected premises in response to the activationof the second decoder by an incoming F2 signal; and circuit meansinterconnecting said first and second decoders for inhibiting the seconddecoder from being activated by an incoming F2 signal until after saidfirst decoder has received an F1 signal.
 10. An alarm system accordingto claim 9, and further comprising means acting between said radioreceiver at the monitoring station and said second decoder forinhibiting the latter from being activated by an incoming F2 signal whensaid receiver receives an intrusion alarm signal from said protectedpremises.
 11. In an alarm system having: intrusion alarmcondition-signalling means at a protected premises; alarm monitoringequipment for receiving alarm signals at a monitoring station which islinked to the protected premises through electrical power lines; andselectively operable means at the protected premises for transmittingsignals over the power lines to the monitoring station to activate themonitoring equipment there to respond to intrusion alarm signals fromthe protected premises; the improvement which comprises: a transmitterat the monitoring station for transmitting a signal over the power linesto the protected premises when the alarm monitoring equipment at themonitoring station is conditioned to respond to intrusion alarm signalsfrom the protected premises; and means at the protected premises forresponding to said last-mentioned signal.
 12. An alarm system accordingto claim 11, and further comprising: means for modifying saidlast-mentioned signal when the alarm monitoring equipment responds to anintrusion alarm signal from said protected premises.
 13. An alarm systemaccording to claim 12, wherein said transmitter at the monitoringstation transmits a distinctive carrier signal over the power lines tosaid protected premises which is unmodulated in the absence of aresponse by said monitoring equipment to an intrusion alarm signal fromsaid protected premises and which is modulated when such a responseoccurs; and said means at the protected premises for responding to saidlast-mentioned signal produces different indications for unmodulated andmodulated signals, respectively.
 14. An alarm system according to claim13, wherein said selectively operable means at the protected premisesmay be operated to de-activate the alarm monitoring equipment at themonitoring station from responding to intrusion alarm signals at saidprotected premises.
 15. In an alarm system having: intrusion alarmcondition-signalling means at a protected premises; alarm monitoringequipment for receiving alarm signals at a monitoring station which islinked to the protected premises through electrical power lines; andselectively operable means at the protected premises for transmiTtingsignals over the power lines to the monitoring station to activate themonitoring equipment there to respond to intrusion alarm signals fromthe protected premises; the improvement wherein said selectivelyoperable means at the protected premises comprises: means for applying acarrier signal to the power lines to be transmitted to the monitoringstation; means for modulating said carrier signal at either of twodifferent frequencies; and selectively operable means for activatingsaid modulating means and for selecting the modulating frequency.
 16. Analarm system according to claim 15, and further comprising means at themonitoring station for receiving the modulated carrier signal comingover the power lines from said protected premises and for respondingseparately to the two different modulating frequencies to condition thealarm monitoring equipment at the monitoring station to respond to alarmsignals from said protected premises.
 17. An alarm system according toclaim 16, wherein said means for responding separately to the twodifferent modulating frequencies is sensitive to the sequence in whichsaid two different modulating frequencies are transmitted over the powerlines from said protected premises to the monitoring station.
 18. Analarm system according to claim 17, wherein said means for respondingseparately to the two different modulating frequencies comprises: afirst decoder that is sensitive substantially only to a first modulatingfrequency, F1; a second decoder that is sensitive substantially only toa second modulating frequency, F2; means coupled to the output of saidsecond decoder for conditioning the alarm monitoring equipment at themonitoring station to respond to intrusion alarm signals from saidprotected premises in response to the activation of the second decoderby an incoming F2 signal; and circuit means interconnecting said firstand second decoders for inhibiting the second decoder from beingactivated by an incoming F2 signal until after said first decoder hasreceived an F1 signal.
 19. An alarm system according to claim 18, andfurther comprising means at the monitoring station operable in responseto receipt of an intrusion alarm signal for inhibiting the seconddecoder from being activated by an incoming F2 signal.
 20. In an alarmsystem having: intrusion alarm condition-signalling means at a protectedpremises; alarm monitoring equipment for receiving alarm signals at amonitoring station which is linked to the protected premises throughelectrical power lines; selectively operable means at the protectedpremises for transmitting signals over the power lines to the monitoringstation to activate the monitoring equipment there to respond tointrusion alarm signals from the protected premises; the improvementwhich comprises means for preventing said selectively operable means foractivating the monitoring equipment at the monitoring station when anintrusion alarm condition already exists at said protected premises.